The overall objective of the proposed research is to elucidate the molecular mechanism of sensory processing in E. coli and S. typhimurium chemotaxis. Sensory-motor regulation in bacteria represents a useful model system for the study of receptor- mediated control of cell behavior. Receptor activity is controlled by 2 enzymes, an S-adenosylmethionine:glutamate methytransferase and a glutamyl methylesterase. Genetic studies have identified 4 additional cytoplasmic proteins required for chemotaxis, the products of the cheA, cheW, cheY, and cheZ genes. The specific goals in this grant period include determining the structure-function relationships which underlie the activities of the receptor modification enzymes. What is the role of the regulatory domain of the esterase? Is a thioester adduct between the receptors and the esterase important in chemotaxis? What is the physiological significance of the methylation reactions in chemosensing? The biochemistry of the auxiliary signalling proteins will also be investigated. Specific projects include determining the role of CheA in the regulation of the methylesterase, determining the possible role of nucleotides in CheW function, and elucidating the mechanism and significance of CheZ methylation. The coordinate functioning of these components will be investigated using a variety of genetic approaches, including the selection of second site mutations which compensate defined lesions in critical structural features of the Che proteins. Finally, attempts will be made to extend results obtained with chemotaxis to cognate regulatory systems in bacteria including the apparatus in B. subtilis which triggers the developmental switch from vegetative growth to endospore formation, and the mechanism in E. coli which regulates porin expression.